This invention relates generally to print heads for data printers or the like and, more particularly, to means for guiding and transporting inked printing ribbons used in such a printing head.
Heretofore it has been conventional to use a laterally-reciprocal printing head having a continuous-loop ribbon cartridge for supplying inked printing ribbon such that the ribbon passes before the printing needles which impact the ribbon to form characters on a printing surface. It is known that providing a 180.degree. twist in a continuous loop-type printing ribbon (i.e., a "Mobius Loop") permits the printing needles or other impact members to strike different portions of the printing ribbon on different passes including both sides of the ribbon. However, the existence of the twist, although desirable for evening out ribbon wear and, consequently, providing for longer ribbon life and improved printing characteristics, can cause jamming problems as the speed of ribbon advance changes and the tension on the ribbon varies, since the twist can become fixed in the ribbon as a fold which travels with the ribbon as the latter is advanced. When this occurs, the least that can happen is that the ribbon no longer is reversed from one side to the other as it is moved along its entire length, and the favorable wear-extending effects of reversal are thus lost. More often, the moving fold representing the twist appears as a thickened, bunched section of ribbon which will snag, catch or jam at some point along the path of ribbon travel, most often breaking or tearing the ribbon or jamming the ribbon transport mechanism and causing not only shutdown of the printer but serious problems or breakage of parts as well. These are some of the problems this invention overcomes.